NAT'L INST OF STAND & TECH 683

176552

IR 77-1401

Processing and Characterization

of NBS Standard Polyethylene

For Use As A Negative Control

Material

Anthony J. Bur

Dental and Medical Materials Section

Polymers Division

Institute for Materials Research

National Bureau of Standards

Washington, D C. 20234

Final Report for Period

September 1, 1976 through August 31, 1977

November 1977

Issued January 1978

Material Science Toxicology Laboratories

University of Tennessee

Memphis, Tennessee 38163

Prepared for

100

.U56

77-1401

DEC 1 2 ^"79

NBSIR 77-1401

PROCESSING AND CHARACTERIZATION

OF NBS STANDARD POLYETHYLENE

FOR USE AS A NEGATIVE CONTROL

MATERIAL

Anthony J. Bur

Dental and Medical Materials Section

Polymers Division

Institute for Materials Research

National Bureau of Standards

Washington, D C. 20234

Final Report for Period

September 1, 1976 thru August 31, 1977

November 1977

Issued January 1 978

Report of work done under contract with the Material Science Toxicology

Laboratories, University of Tennessee.

Prepared for Material Science Toxicology Laboratories

University of Tennessee

Memphis, Tennessee 38163

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler, Acting Director

INTRODUCTION

The continuing development of new polymeric materials with wide ranging

physical properties gives the biomedical engineer extensive latitude in

design and application of these materials. One crucial criterion, which

these materials must satisfy, is biocompatibility with cardio-vascular

and/or intramuscular tissues. Many polymers, which otherwise have desirable

physical properties, are eliminated by the biocompatibility tests. These

tests are conducted routinely in scores of biomedical laboratories by implantation of polymer test specimens into laboratory animals ."'"At the

present time inter-laboratory comparison of these data is difficult or

impossible because control and standardization of the tests on a national

scale does not exist. Parameters such as quality, species and diet of the

animals are impossible to control and therefore it becomes necessary to

"calibrate" each animal during the test. This internal calibration can

be accomplished by using a negative control material which is implanted

in the animal along with the test specimen. Data is then recorded as

tissue reaction to the test specimen relative to its reaction to the

control material. If all laboratories use the same negative control', a

common reference can be maintained and interlaboratory comparison of data

becomes possible.

We describe here the participation of NBS in the development of a

candidate negative control material. The source of this material is two

large batches of polyethylene whose physical properties have been characterized by the NBS Polymers Division. They have been certified by NBS as Standard

Reference Materials (SRM) 1475 and 1476. Lists of some of their physical

properties are contained in Appendices A and B. The 1475 SRM is a high density,

1
highly crystalline, linear polyethylene. The 1A76 SRM is a low density,

highly branched polyethylene with low crystallinity

As indicated above and in appendices A and B, "polyethylene" can be

made with different physical characteristics. Parameters such as molecular

weight, distribution of molecular weight, density, branching and crosslinking can be cheinged with corresponding changes in physical properties.

In addition, each manufactured batch will have its own residual catalyst,

trace elements, and anti-oxident additive. Thus, a material designated only

as "polyethylene" is far from completely characterized. The manner in which

the above parameters effect the biocompatibility is unknown, but it would be

prudent to draw negative control specimens from a single uniformly processed

batch.

Polyethylene has been widely used as an implant material, particularly

2 3 for hip and knee prothesis *

. It is known that tissue reaction to it is

minimal. Also, it is being used routinely as a negative control material by

biomedical laboratories which have their own in-house standards. The existing

situation has resulted in a proliferation of in-house standards and presents

a major obstacle to inter-laboratory comparison of data. Should the NBS

polyethylene prove to be a suitable negative control, then a single source

would be available for all biomedical laboratories for some years to come. EXPERIMENTAL PROCEDURE

Fabrication of Sheet and Rod Samples

The 1475 and 1476 SRM material was polymerized in the form of small

spherical pellets approximately 3.2 mm in diameter. While these pellets could

be used for tissue culture tests, they are not large enough to use as controls

for in vivo testing of large components such as orthopedic implants. The
material was processed Into larger sizes by using standard extrusion and

compression molding equipment. Typically, this equipment dictates that

the shape of the product be either a rod or sheet. It was decided that

suitable dimensions for laboratory work would be rods, 1.59 mm (1/16")

diameter x 15 cm length and sheets, 16.5 cm square x 0.5 mm thick. This

fabrication was carried out at Drexel University, Philadelphia, PA because

their materials laboratory has the equipment to work with relatively small

quantities (10-20 kg) of polyethylene and because they could fabricate both

rods and sheets in the same laboratory.

Each sheet was compression molded individually using a molding form which

had aluminum faces. In order to avoid unnecessary contamination of the

sheet surfaces no mold release lubricant was used. The pellets were added to

the mold which had been previously heated In a hydraulic press to 175 °C for

the i476 and to 210*'C for the 1475. The 1476 pellets were compressed at

175°C ufider a pressure of 2.41 x 10 N/m^ (350 psi) for 5 minutes and then

cooled under pressure to room temperature in 10 minutes. The 1475 pellets

were compressed at 210°C under the same pressure (350 psi) for 2 minutes

and then cooled under pressure to room temperature in 10 minutes.

Only the 1476 material was made into rods and this was accomplished

using an extruder. With this machine, pellets are screw-fed through a

heated channel and through an orifice of 1. 59mm(l/16") diameter. The temperature of the pre-exit channel as well as the orifice was kept at 150°C.

Immediately after exit from the extruder, the filament was quenched by drawing

into a bath of distilled water at room temperature. Having obtained operating

temperature and an acceptable draw rate, the extruder was run continuously

until 45.7 m (150 ft) of filament or rod were extruded. The rod was then

cut into 15 cm lengths.

3
Prior to characterization, loose contaminants on the surface of the

samples were removed by washing them in a dilute solution of

detergent in distilled water (100 mg per litre). A camel's hair brush was

used to wipe the surfaces during washing, after which the samples were

thoroughly rinsed with distilled water. No organic solvents were used for

cleaning because it is known that such small molecules can diffuse into

polymeric solids.

Characterization of the Sheets and Rods

It was essential that the fabricated samples he monitored because, as

candidate negative control materials, uniformity of the samples is needed.

Although the pellet material is well-characterized, most of the measurements in

Appendices A and B do not apply after the pellets have been processed into

sheets and rods. In addition, the surfaces of the sheets and rods, being

the interface with the biological tissues, need to be investigated with

regard to uniformity and the presence of contaminants.

The surface measurements consisted of attenuated total reflectance

(ATR) infra-red absorption, contact angle observations, and secondary ion

emission mass spectroscopy (SIMS) . The first two methods can be classified

as macroscopic investigations because the results are obtained from a relatively large area of the surface. The SIMS measurement is an elemental

analysis of a small area of the surface, 200 microns square.

The contact angle measurements were obtained using a Rame-Hart contact

angle apparatus. This equipment consists of a light source, sample chamber,

and microscope mounted in horizontal alignment on an optical bench. Droplets

of liquid are placed on the surface by using a microsyringe. The contact

angle is measured by rotating the cross hair in the microscope to correspond to the tangent of the angle of contact between liquid and solid. In

this case droplets of distilled water were used.

* See footnote page 13 ,
The ATR infra-red measurements were made using the Perkin-Elmer 337 Infracord which was adapted for ATR measurements with a Wilks ATR lens and mirror

system. The infra-red absorptions are measured by observing the infra-red

light which has undergone multiple reflections from the surface of the test

specimen. This light penetrates only several microns into the sample, so that

it is the molecular character of the surface and near surface which determines

the IR spectra. The surface area of polyethylene sheets from which the spectra

was obtained was 4.5 cm x 3.0 cm. For the rods, the ATR spectra was obtained

from 26 sections of rod 4.5 cm in length which were aligned parallel to one

another and pressed against the lens which is used as the reflecting medium.

The SIMS measurements were carried out by the Analytical Chemistry Division

at NBS. The instrument is a mass spectrometer which analyzes secondary ions

ejected from the sample surface as a result of bombardment with accelerated

argon ions. The sampling volume is usually several hundred angstroms deep

by 200 microns square. Absolute measurements of the concentration of trace ^

elements are not directly obtainable from the SIMS data. An internal

standard » such as a dopant of known concentration, must be incorporated in

the sample and all other measurements can be referred to this. For the

polyethylene sheet and rod, we did not have the resources to do this so that

the results are limited to a qualitative indication of the presence of the

observed elements and to a relative comparison of results from different samples.

In addition to the above, several bulk characterizations of the sheet

and rod were made. These measurements included density, differential scanning

colorimetry (DSC) , and infra-red transmission spectra. The density measurements

were carried out using a density column which was formulated with distilled

.water and ethyl alcohol according to the ASTM D1505 procedure^. The column was

5
calibrated with small glass beads of known density. The DSC was used to

qualitatively observe the melting and annealing characteristics of the

samples and to assess the uniformity of the material from specimen to

specimen. A Perkin Elmer DSC-2 instrument was used over a temperature

range from 10°C to ISO'C.

RESULTS AND DISCUSSION

The total number of specimens which were examined for this program was

40 sheets and 150 rods, of which 3A sheets and all 150 rods were processed

from the 1476 material. Sheets processed from 1476 material were numbered

76-1, 76-2, etc., thru 76-34. The other six sheets are from the 1475 polyethylene and these are designated as 75A and 75D thru 75H. The 150 rods

were considered as parts of a single sample since they were extruded in a

single process. These 150 rods are not handled individually, but rather a

set of 30 rods was selected at random and these were used in the characterization experiments.

From each sheet, a 1.2 7 cm wide strip was cut from two adjacent sides

and retained for the characterization measurements. Each large sheet and

side strip was used for the contact angle measurements but in order to avoid

contamination only the side strip was used in the other experiments. Upon

completion of the measurements, the sheet was made available for biocompatibility

studies and stored in a paper folder. The side strip, also stored in paper,

was retained for additional materials study. Paper was used as a storage

medium in order to avoid contamination from small organic molecules which are

often present in commercially processed plastic packaging material.

Contact Angle Measurements

Using distilled water droplets, the contact angle was measured for both

surfaces of all 40 sheets. Thirty to forty contact angle measurements

were made for each side or a total of 60 to 80 measurements per sheet. The
Average and standard deviation of the contact angle for each sheet is listed

in Table 1. Taking all thirty-four sheets of the 76 series, the average

contact angle is 90.8° ± 1.8°. For the six sheets of the 75 series, the

combined contact angle is 91.8° ±1.8°. A value of 94° for water droplets

4 5 on polyethylene was obtained by Zisman and coworker '

, but the limit of

accuracy and standard deviation of their measurements was not given.

Considering the precision and standard deviations normally encountered

in contact angle measurements, it is likely that there is no significant

difference between our measurements and those in the literature. The

existence of some surface differences can not be ruled out, however. For

example, a monolayer film of a metallic oxide would be a high energy surface

and would allow the water droplet to spread more than on a polyethylene surface .

Also, the differences in surface roughness can influence the contact angle.

It must be remembered that these measurements are macroscopic and do not give

us information about small amounts of surface contaminants.

For the rods, ten samples were selected at random for the contact angle

measurements. These ten samples can be considered as different pieces of a

single sample since the rods were extruded in one continuous filament and

then cut into 15 cm lengths. During the measurement the rod was oriented

perpendicular to the axis of the microscope light beam. The droplet was

placed so that it symmetrically straddled the top of the rod. The angle

which was measured was the angle between droplet and rod at the very top

of the rod while looking transverse to the axis of the rod. At this point

7
the effect of gravity in deforming the droplet is least and comparison

with the results from a flat surface are possible. This was tested by

measuring the contact angle on a flat sheet and then at the apex after

the sheet was bent into a 1 cm diameter circle. No significant difference

was found before and after bending.

The results of the contact angle measurements on the rods are shown

in Table II. The numbers are seen to be in agreement with those obtained

from the sheets. The average for all the rod data points is 91.1° + 0.7°.

Considering that the estimated uncertainty in each measurement is ± 0.5**,

this result indicates the presence of macroscopic surface uniformity.

The rod contact angle is reasonably close to the 94° expected for polyethylene, and the slightly depressed value cannot be attributed to material

contamination which has been observed in the SIMS measurement. These results,

which are discussed below, show that the rod samples have the highest amount

of elemental surface contamination.

ATR Infra-Red

The results of a representative ATR scan for the sheets or rods processed

from the 1476 material are shown in Figure 1. For sheets processed from the

1475 material, a spectrum is shown in Figure 2. In both cases, the spectra

are typical of polyethylene with the only differences occurring in the vicinity

of 1350 cm~^. Here, the CH^ end groups, which are more numerous in the

branched 1476 polymer than in the linear 1475 poljmier, show absorption in

Figure 1 but not in Figure 2. At 700 cm ^, the typical crystalline amorphous

doublet of polyethylene showed some variation fram sample to sampM but

this was attributed to a polarization effect associated with this band.

During the infra-red scan special attention was paid to the regions

where carbonyl groups absorb (1750 cm"''") and to the region 400-800 cm"-'-

8
where metallic oxides absorb. No evidence of oxidation of any kind, carbonyl or metallic, was found in the infra-red spectra. The observations

were uniform and typically polyethylene;

Secondary Ion Mass Spectroscopy (SIMS)

The SIMS measurement is more sensitive to the presence of elemental

contaminants than is either the contact angle or infrared measurement. Unfortunately, only qualitative information has been obtained because the calibration procedure is an extensive one requiring the preparation of standard

samples. We are, however, able to compare the results from sample to sample

and to see differences between pallet, sheet and rod. Analysis was carried

out on eight samples, 5 sheets, 2 rods and one pellet.

The results are shown in Figures 3 thru 5, in which typical plots of

detector response versus the ratio of mass to charge, M/e, are shown. The

simplest spectra belongs to the pellet, which is the unprocessed polyethylene.

More complex spectra are seen for the sheet and rod. It is apparent that

processing, particularly extrusion, is a source of additional contamination

which is not seen in the pellet. In the case of the pellet, it is possible

to identify all of the peaks, but for the rod samples the spectra was too

complex to identify every peak. It is clear that metallic oxides, SiO and

FeO, are present on the surface of the rod. Macroscopically the sheet and

rod appear to be the same, but it is obvious from these data that the elemental

contamination is quite different.

The data for all eight samples are presented quantitatively in Tables HI

and IV. The numbers in these Tables are the ratio of ion intensity to the

carbon 12 ion intensity. Here carbon is taken as the reference ion because,

as an essential element in the polyethylene matrix, its intensity would be

a constant for all samples. Note that the numbers can not be related to

absolute composition because calibration standards for polyethylene are not

9 available.
The SIMS results for the rods were somewhat unexpected because there

was no indication of contamination from any of the other measurements. The

extrusion apparatus had been thoroughly cleansed prior to processing but no

analytical check on the extruded product was made until the SIMS measurement

months later.

Density Measurements

The results of the density measurement for the sheets and for fifteen

rod samples are shown in Table v. It is noteworthy that all of the sheets

of a given series are, within the limits of accuracy of the measurement,

identical. This result indicates that the temperature-pressure cycle which

was used for the preparation of the sheets was uniformly the same for each

3

sheet. The density of the rods, 0.9210 + 0.0003 g/cm was slightly lower

than the 76 sheets because the rods are quenched rapidly to room temperature

as the material exits from the extruder while the sheet is cooled to room

temperature under pressure over a period of 10 minutes.

Differential Scanning Calorimetry (DSC)

DSC was carried out on several samples of the 75 and 76 series. Typical

heating and cooling cycles for these samples are shown in Figures 6 and 7.

For sample 75A, the DSC curves show simple melting and crystallization with

a melting temperature of 134°C (407K) . For sample 76- 14, however, the DSC

curves are more complicated. On the initial heating run a small

transition is observed above room temperature at 47°C (320K). On the subsequent heating run, which was started only 20 minutes after the one in

Figure 7, this transition was absent. Further investigation, e.g. annealing

at 60°C, demonstrated that the 47^0 transition was due to the melting out of

crystals which were formed during storage at room temperature over a period

of several months. The sample is continuously undergoing "annealing" even

at this low temperature. This is a very small bulk crystallization which

10
probably has little effect on the surface of the material.

The crystallization run is seen In Fig. 7 (b) where the sample is taken

from 430K to 300K. The principle crystallization transition occurs at 103C

(376K) , and there is a secondary crystallization at 68C (3A1K) . Subsequent

cycling at different heating and cooling rates showed that this secondary

transition was a true crystallization phenomenon and not a kinetic artifact.

This 68 C transition is also present in the DSC curves for the 1476 pellet.

We speculate that it is due to the crystallization of short side branches in

the 76 material. This transition is not observed in sample 75A which has

very little branching.

CONCLUSIONS

The macroscopic observations, contact angle, ATR-IR, density and DSC

show that, within the precision of these measurements, the sheet and rod

samples are uniform. The small difference in density between the sheet

and rods of the 76 series, 0.9260 g/cm-* versus 0.9210 g/cm , arises because

quenching the extruded rod results in a lower rod density. There is no

evidence of macroscopic contamination in the observations.

The SIMS apparatus, as an analytical tool, is far more sensitive than

the above experiments. It is possible to trace the contamination which is

added to the material during processing from pellet to rod and from pellet to

sheet. In spite of this, the SIMS data show that there is a measure of

uniformity in the resultant product. It is suggested that the contamination

is uniformly imparted to the samples. Of the five sheets, there is a similar

in the relative amounts of and the species of elements which are present.

Although the elemental analysis of the rods is significantly different from

the sheet, the SIMS results for the two rods are similar.

11
The differences in the SIMS analysis of the sheet and rod arise because

of the different methods of manufacturing, compression molding for the sheets

and extrusion for the rods. For the subsequent bio-compatibility studies,

it is important to know that these differences exist so that potential

correlations of data can be understood.

Other conclusions come from our experience in dealing with the processing

of polyethylene. In this case, two kinds of polyethylene were available, one

a high density linear polymer (1475) and the other a branched low density

sample (1476). Molding the high density material into uniformly flat samples

was difficult because contraction during crystallization caused a visible

variation in surface texture. It is not known whether this is harmful in

terms of biocompatibility , but there is an obvious difficulty in controlling

the macroscopic surface uniformity. On the other hand, molding of the low

density 76 series sheets resulted in visible uniformity for the samples.

From a processor's point of view, the biggest difference between compression

molding and extrusion is economics. Compression molding requires detailed

preparation, and cycling of temperature and pressure, all of which take several

hours for each sample. For the rods, however, once the extruder has been

flushed and cleaned, the machine can be fed continuously while extruding rods

in one long filament. The efficiency of the extrusion machine makes it a

practical method of processing large quantities of material. For laboratory

studies involving tissue culture analysis, a large quantity of negative control

material is often used and extrusion is the only practical method of processing

the material.

12
If biocompatibllity tests demonstrate the suitability of this material

as a negative control, proper attention must be given to methods of processing

and the elemental contamination which results. It is apparent from these

tests that only a sensitive analytical tool such as SIMS can be used to

observe the differences between surfaces of these polyethylene samples.

ACKNOWLEDGEMENTS

The author wishes to acknowledge the assistance of Prof. Ihab Kamel

and Mr. George Halldin at Drexel University, who processed the sheet and

rod material in their laboratory. Also, acknowledgements are due to

Dr. Dale Newberry of the NBS Analytical Chemistry Division who made the

SIMS measurements.

*Certain commercial materials and instruments are identified in this report

to adequately specify the experimental procedure. In no instance does such

identification imply recommendation or endorsement by the National Bureau

of Standards, nor does it imply that the material or instrument identified

is necessarily the best available for this purpose

13
References

1. See, for example, J. E. Turner, W. H. Lawrence and J. Autian,

J. Biomed. Mat. Res., 1, 39(1973).

2. J. Chamley, Clin. Orthop. Related Res. 72., 7(1970).

3. E. Englebrecht, Excerpta Med. 298 , 33(1973).

4. W. A. Zisman in "Contact Angle Wettability and Adhesion", Advances

in Chemistry Series No. 43, Publ. by American Chemical Society,

Washington, D. C. , 1964, p 13 and 149.

5. H. Schonbom in "Encyclopedia of Poljnner Science and Technology",

Vol. 13, p 549, J. Wiley and Sons, New York, NY 1970.

6. Annual Book of ASTM Standards, Part 35, p 507, Test D1505, American

Society for Testing Materials, Philadelphia, PA 1977.

7. M. P. Groenewege, J. Schuyer, J. Smidt and C. A. F. Tuynman in

"Crystalline Olefin Polymers", Part I, Edited by R. A. V. Roff and

K. W. Doak, Interscience Publ., New York, NY 1965, Chapt 14.

14
Table I. Contact Angle for Water Droplets

on Polyethylene Sheets.

Sample Angle Sample Angle

(degrees) (degrees)

76-1 90.1 ± 1.4 76-21 91.7 ± 2.0

76-2 89.9 ± 1.7 76-22 91.2 ± 1.5

76-3 91.2 ± 1.2 76-23 92.5 ± 1.9

76-4 90.7 ±1.9 76-24 91.9 ± 2.3

76-5 90.4 ± 1.7 76-25 92.9 ± 1.5

76.6 92.3 ± 1.3 76-26 91.4 ± 2.1

76.7 89.9 ± 2.9 76-27 92.6 ± 1.7

76-8 90.6 ± 1.8 76-28 92.2 ± 2.0

76-9 91.3 ± 2.0 76-29 92.0 ± 1.4

76-10 93.0 ± 1.8 76-30 92.0 ± 1.1

76-11 90.5 ± 0.8 76-31 92.5 ± 1.6

76-12 90.7 ± 1.1 76-32 91.2 ± 1.5

76-13 90.4 ± 1.3 76-33 89.9 ± 2.4

76-14 90.8 ± 0.9 76-34 92.0 ± 1.5

76-15 91.7 ± 2.0 75A 90.5 ± 0.8

76-16 89.8 ± 1.8 75D 91.7 ± 1.8

76-17 90.9 ± 1.8 75E 91.9 ± 1.8

76-18 92.0 ± 1.7 75F 92.3 ± 1.7

76-19 91.2 ± 2.0 75G 91.8 ± 1.8

76-20 90.9 ± 1.0 75H 91.5 ± 1.8

15
Table II. Contact Angle for Water Droplets

on Polyethylene Rods.

Sample Angle Sample Angle

(degrees) (degrees)

1 91.0 ±0.6 6 91.2 ± 0.7

2 91.1 ± 0.6 7 91.0 ± 0.7

3 91.0 ± 0.8 8 91.0 ± 0.7

4 91.2 ± 0.5 9 91.0 ± 0.6

5 91.3 ± 0.7 10 91.0 ± 0.6

16
Table III. Normalized Secondary Ion Signals

12 +

(all signals normalized to C )

Sheet Samples

Ion 76-2 76-3 76-4 76-20 75A Pellet

1476

V 0.25 0.50 0.77 0.73 0.26 1.5

CH"^ 0.037 0.061 0.045 0.13 0.10 0.09

^^n"*" 0.030 0.020 0.033 0.05 0.018 0.031

'^O''' 0.033 0.019 0.044 0.022 0.024 0.010

^^Na"*" 0.032 0.057 0.053 0.05 0.134 0.009

^^Mg"*" 0.055 0.102 0.153 0.1 0.166 0.026

^^Al"^ 0.378 0.314 0.291 0.45 1.39 0.040

^^Si"*" 0.166 0.202 0.263 0.28 0.55 0.051 ~ — — 0.038 0.044

^^Ca"*" 0.106 0.097 0.135 0.06 0.38 0.022

48 4- ^^^Ti ~ ~ — — 0.038

^^Cr''' — 0.022 0.019 — 0.007

^Se"*" ~ 0.039 0.039 0.02 0.045 0.009

17
Table IV. Normalized Secondary Ion Signals

(all signals mormalized to -^^C )

Rod Samples

Ion Rod 1 Rod 2 Pellet

1476

1. 4 0.75 1.5

- 0.0053 -

0. 25 0.2 3 0.09

U. 084 0.14 0 . 031

0. 12 0.23 0.010

0. 19 0. 38 0. 0088

0. 39 0.65 0.026

0. 3 5 0. 88 0.04 0

1. 8 1.28 0.051

0. 061 0.25

0. 24 0.56 0. 022

0. 0048 0.017

0. 23 0.21 - 0.0088

18
Table V. Density of Polyethylene Sheets and Rods

Sample

75A, 75D thru 75 H

76-1 thru 76-3A

76 ROD (16 pieces)

P

gTcnP

0.9632 ± 0.0005

0.9260 ± 0.0005

0.9210 ± 0.0003

19
ai: # t Figure Captions

Figure 1. Attenuated Total Reflectance Infra Red Spectra for Sample

76-10. This spectra was typical for all sheets and rods of the

76 series.

Figure 2. Attenuated Total Reflectance Infra Red Spectra for sample

75A. This spectra was typical for all sheets of the 75 series.

Figure 3. Trace of the SIMS data for a pellet of the NBS 1476 standard

reference polyethylene material.

Figure 4. Trace of the SIMS data for the compression molded sheet

sample 76-20.

Figure 5. Trace of the SIMS data for a piece of extruded 76 rod.

Figure 6. (a) DSC melting curve for sample 75A;

(b) DSC crystallization curve for sample 75A.

Figure 7. (a) DSC melting curve for sample 76-14;

(b) DSC crystallization curve for sample 76-14.

20
(U

o

a,B CO

(3 -a

t/5 oM

M

O 13

(0M CO 4J 4-t cj (U

0) 0) a ^ C/) CO

0) i-l

CO »-i M O

c

cao

>,

i-i

CO

Cfl

CCJ u

*-> CJ

0)a.

CO

CO

a

CO u

o

3)

•X3 X • a) H CO

CO -H 3 . M

C O (U

0) iH CO W I < r-~

3

rl

(aiV3S AUVUilSUV)

21
22
u

c

nJ u

(0 vO

z

0)a CO

1-1

o eg

CO 0)

CO >,o

o.

o

0)

0)

<4-l 0)

0)3

CO

(aieas 6o|) 3SN0dS3U U013313a

23
u

(Si 0) XI

(0 •a

(U T3rHO

0

tiO

•H

CO

CO

0)M

a

o

o

0)

4-1 M

O

CO

OJ o

•u I v£) o

(U iH

cd a

l-i c4 H CO

3

00

•H

(3|eas 6o|) 3SNOdS3a U0i33i3a

24
25
T r T

1 r

SAMPLE 75 *

OSC CURVe HUTING RATE W/min

HEATING

300 320 340 360 3«0

TEMPERATURE. K

400 420

Figure 6. (a) DSC melting curve for sample 75A;

SAMPLE 75 A OSC CURVE COOLING RATE 10° /min

COOLING — (b)

i 1

1 1 • 1 1 1 1 410 390 370 350 TEMPERATURE. K

330 310

Figure 6. (t>) DSC crystallization curve for sample 75A.

26
I 1 1 1 1 f T -r 1 1

SAMPLE 76 - 14

DSC CURVE

HEATING RATE lOVnun.

47 C

k -

-"^ HEATING — Its r lib t

1 1 1

1 i 1 1 1 1 300 320 340 360 380 400

TEMPERATURE. K

Figure 7. (a) DSC melting curve for sample 76-14;

1

... , 1 103 C —r [ 1 1 1

1 —

1 68 C

SAMPLE 76 - 14

DSC CURVE

COOLING RATE 1Q°/min

COOLING * (b)

1 1

1 1 1 I I 1 1 380 360 340 320 300 TEMPERATURE. K

gure 7. (b) DSC crystallization curve for sample 76
Appendix A

The following data was obtained for the 1475 polyethylene pellet

material. The experiments and data analysis were carried out by NBS

Polymers Division Staff consisting of C. A. J. Hoeve, H. L. Wagner,

J. E. Brown, R. G. Christensen, L. J. Frolen, J. R. Maurey, G. S. Ross,

and P. H. Verdier.

Standard Reference Material 1475 Linear Polyethylene

Quantity Average

Values

Estimated

Standard Deviation

of Average

Molecular Weight

Wei^t-average molecular weight 52,000 2,000

Number-average molecular weight

Weight-average molecular weight

Z-average molecular weight

Ratio of molecular weights M :M,, :Mn

18,310

53,070

138,000

7.54:2.90:1

360

620

3,700

Limiting Viscosity Number (<ll/p) In l-chlororiaphthalene at l.iO'^'d In 1,2,4-trichlorobcn/cne at 130 °C

In decahydronaphthalene atl30°C

0.890

1.010

i.l80

0.0032

.0086

.0032

M. lt-FIow Rate(g/10 min) 2.07 .0062

Density (g/cm') 0.97844 .00004

28
Appendix B

The following data was obtained for the 1476 polyethylene pellet

material. The experiments and data analysis were carried out by NBS

Polymers Division Staff consisting of C. A. J. Hoeve, H. L. Wagner,

J. E. Brown, R. G. Christiansen, and J. R. Maurey.

Standard Reference Material 1476 Branched Polyethylene

Quantity

Limitinfi; Viscosity Niinihcr (dl/fi) In 1-cliloronaplilliaIcne at IM)^(.

In l,2,4-lrichlor()l.rn/.cnc at In dccalin> at 1 30 °C

Melt Index (g/IO min)

Density (g/rm3) at 23 "C

Avorapo

Valnrs

0.8132

.9024

1.042

1.19

0.9312

F.stimale

of

Precis ion

().oo;5;5 .()o;u

M)22

.010

.0006

29
NBS-114A <REV. 7 73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PL;HI.I( ATION OR REPORT NO.

77-1401

2. Gov't Accession

Mr. L>* O.

4. i n I f-: AND SL'HTITLE

Processing and Characterization of NBS Standard Polyethylene

for Use as a Negative Control Matprlal

5. Publication Date January 1978

6. Performing Organization (.oJ<-

7. AUIMORlS)

Anthony J. Bur

R t-^ r t /"A r TT\ inn llrf»in r<<ar\/^rf M

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 3110118

11. Contract /Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Materials Science Toxicology Laboratories

College of Dentistry and College of Pharmacy

University of Tennessee Medical Units

Memphis, TN 38163

13. Type of Report & Period Covered ^^^^^ Report

9/1/76-8/31/77

14. Sponsoring Agency < ixic15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less (actual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

This work was initiated in order to fulfill a need for a polymer which can serve

as a negative control material for biocompatibility studies involving new polymer implant materials. Two large batches of well-characterized polyethylene resin are the

sources of the candidate negative control material. The original polyethylene resin,

in pellet form, was processed into sheets and rods and examined for surface con- taminants and uniformity. Surface observations consisted of measurements of

contact angle, attenuated total reflectance infra-red absorption and secondary ion mass spectroscopy (SIMS). Bulk measurements consisted of density, differential scanning

calorimetry , and transmission infra-red spectroscopy. All of the measurements,

except SIMS, indicated that the material was uniform and typically polyethylene with no macroscopic contamination. The SIMS measurement, which is a sensitive analytical tool

for detecting low levels of elemental contamination, showed significant differences

between the type, of contamination on the surfaces of the starting material and the type

of contamination on the processed sheet and rod. The method of processing was also

significant because the extruded rod showed much more contamination than did the compres

sion molded sheet. The surfaces of the rod were found to contain metallic oxides and

several other metals which were not present in the unprocessed polyethylene. It is con- cluded that close attention must be paid to the method of processing and that only a sensitive analytical tool such as SIMS can be used to detect surface contamination and

the differences between these samples.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons) Riomaterials ; negative control ; polyethylene; processing sheets

and rods; surface characterization; surface contamination.

18. AVAILABILITY

^

Unlimited 19, SECURITY CLASS

(THIS REPORT)

21. NO. OF PAGES

1 !• or Official Distribution. Do Not Release to NTIS

UNCLASSIFIED 32

[

' Order iTom Sup. of Doc, U.S. Government

Washinsion. D.C. 20402. SD Cat. No. CU

Printing Office 20. SEC URITY CLASS

(THIS PAGE)

22. Price ^ Order 1- rom National Technical Information

Springfield, Virginia 22151

Service (NTIS)

unc;lassified $4.50

USCOMM-DC 29042-P74